Techniques for virtualizing a storage device and providing it to a host computer connected with the storage device via a network are described in such documents as Japanese Patent Laid-open No. 2000-339098 (Patent Document 1) and U.S. Pat. No. 6,216,202 Specification (Patent Document 2).
Also in Japanese Patent Laid-open No. 2001-350707 (Patent Document 3), a technique is disclosed which compares evaluated performance values of each storage or each storage region with the required performance values specified by the system administrator and, based on the result, allocates storage regions to a host computer.
Further U.S. Pat. No. 6,131,150 (Patent Document 4) discloses a technique called buddy algorithm (hereinafter abbreviated as B.A.). B.A. is a method for preventing fragmentation of vacant regions in a memory. By managing the memory in such a manner that the allocated memory size is always a power of two, fragmentation can be prevented since released memory regions can be re-integrated with adjacent vacant regions.